Dts/pts backward extrapolation for stream transition events

ABSTRACT

In one method embodiment, receiving a video stream comprising a first compressed picture without associated time stamp information and a second compressed picture having associated first time stamp information, the second compressed picture following the first compressed picture in transmission order; deriving second time stamp information based on the first time stamp information; and processing the first compressed picture based on the second time stamp information.

RELATED APPLICATION

This application is a Continuation of co-pending U.S. application Ser.No. 12/569,982 entitled “Decoding Earlier Frames with DTS/PTS BackwardExtrapolation” filed Sep. 30, 2009, which issued on May 20, 2014 as U.S.Pat. No. 8,731,000, which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to video processing.

BACKGROUND

Transmission of digital audiovisual content to customer premises isaccomplished today according to a variety of mechanisms, ranging fromtransmission across traditional cable and satellite television networksto computer networks (e.g., Internet Protocol Television or IPTV) wheredigital television services are provided using Internet protocol(broadband). At the customer premises, a digital receiver comprisesfunctionality to receive and decode the digital audiovisual content andprocess for presentation the reconstructed video and/or audio on adisplay and sound component or generally a multi-media device. Certainstream transition events associated with the transmission of digitalaudiovisual content may impose delays in the decoding and presentationof the transmitted content.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the disclosure can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a block diagram that illustrates an example environment inwhich time stamp extrapolation (TSE) systems and methods can beimplemented.

FIG. 2 is a block diagram of an example embodiment of a video streamreceive and process (VSRP) system comprising an embodiment of a TSEsystem.

FIG. 3 is a block diagram that illustrates an example sequence ofcompressed pictures of a video stream in transmission order received andprocessed by an embodiment of a TSE system.

FIGS. 4A-4B are block diagrams that illustrate various embodiments ofbackwards extrapolation periods (BEPs) that serve as a basis forcomputing extrapolated time stamp information.

FIG. 5A is a block diagram that illustrates reconstructed picturesgenerated from the example sequence in FIG. 3 based on unexpired,extrapolated time stamp information.

FIG. 5B is a block diagram that illustrates reconstructed picturesgenerated from the example sequence in FIG. 3 based on a portion ofextrapolated time stamps.

FIG. 6 is a flow diagram that illustrates one example TSE methodembodiment.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

In one method embodiment, receiving a video stream comprising a firstcompressed picture without associated time stamp information and asecond compressed picture having associated first time stampinformation, the second compressed picture following the firstcompressed picture in transmission order; deriving second time stampinformation based on the first time stamp information; and processingthe first compressed picture based on the second time stamp information.

Example Embodiments

Disclosed herein are various example embodiments of time stampextrapolation (TSE) systems and methods (collectively, referred toherein also as a TSE system or TSE systems) that comprise logic (e.g.,hardware, software, or a combination of hardware and software)configured to receive and cache (e.g., buffer) compressed pictures of avideo stream, a portion of which do not possess or are otherwise notassociated with time stamp information (e.g., presentation time stamp(PTS), decoding time stamp (DTS), or a combination of both), determine abackwards extrapolation period (BEP) based on the reception of timestamp information received subsequent to those pictures unassociatedwith time stamp information, backwards extrapolate the received timestamp information to compute time stamp information for the picturescorresponding to the BEP, and decode and provide for presentation (orother processing and/or destination) one or more of the decoded picturespossessing the extrapolated time stamp information.

Various scenarios may arise where backwards extrapolation of PTS/DTSvalues from explicitly received PTS/DTS values to obtain extrapolatedPTS/DTS values may reduce decoding and/or presentation delays andimprove viewer experience in the reception of audio, video, and/or dataservices (collectively or individually also referred to herein as mediacontent). For instance, responsive to a video stream transition eventsuch as a channel change in an Internet Protocol Television (IPTV)network environment, a digital receiver may not receive PTS/DTS valuesfor a received intra-coded (I) picture needed to decode the compressed Ipicture (and any subsequent dependent compressed pictures, which aretypically discarded when received without associated time stampinformation), which may result in a delay period corresponding to thetime to receive an I picture whose PTS/DTS information is explicitlyprovided in the video stream.

Another example scenario is where I-pictures are transmitted lessfrequently, such as for bit-rate reduction. Even if all I-picturespossessed explicit PTS/DTS information, delays may result due to thefact that pictures received prior to the I-picture may not be decodable.

An additional scenario may arise in application-specific or proprietaryimplementations that deviate from standards or specifications in thefrequency of inclusion of time stamp information in the video stream.

By performing backwards extrapolation to compute time stamp informationfor one or more frames responsive to a stream transition event, decodinglogic is enabled to start decoding and processing for presentationcompressed pictures that otherwise may have been discarded, hencereducing delays associated with the stream transition event or otherwiseproviding additional benefits.

These and/or other features, among others, are described hereinafter inthe context of an example subscriber television network environment,with the understanding that other multi-media (e.g., video, graphics,audio, and/or data) environments may also benefit from certainembodiments of the TSE systems and methods and hence are contemplated tobe within the scope of the disclosure. It should be understood by onehaving ordinary skill in the art that, though specifics for one or moreembodiments are disclosed herein, such specifics as described are notnecessarily part of every embodiment.

FIG. 1 is a block diagram of an example environment, a subscribertelevision network 100, in which certain embodiments of TSE systemsand/or methods may be implemented. The subscriber television network 100includes one or more video stream emitter systems, such as video streamemitter (VSE) system 102, coupled to one or more video stream receiveand process systems, such as video stream receive and process (VSRP)system 106, over a communications medium 104. The VSRP system 106 isfurther coupled to a display device 108. In one implementation, thedisplay device 108 is configured with an audio component (e.g.,speakers), whereas in some implementations, audio functionality may beprovided by a device that is separate yet communicatively coupled to thedisplay device 108 and/or VSRP system 106. The VSRP system 106 furtherincludes a time stamp extrapolation (TSE) system 200, which is explainedfurther below. Note that in some embodiments, functionality of the TSEsystem 200 may be incorporated elsewhere in the subscriber televisionnetwork 100, such as in display device 108.

The subscriber television network 100 may comprise an IPTV network, acable television network, a satellite television network, or acombination of two or more of these networks or other networks. Further,network PVR and switched digital video are also considered within thescope of the disclosure. Although described in the context of videoprocessing, it should be understood that certain embodiments of the TSEsystems 200 described herein also include functionality for theprocessing of other media content such as compressed audio streams.

The VSE system 102 comprises one or more servers, routers, and/orswitches (e.g., at the network edge, among other locations) that processand deliver and/or forward (e.g., route) various digital services tosubscribers. Such digital services may include broadcast televisionprogramming, video-on-demand (VOD), pay-per-view, music, Internetaccess, commerce (e.g., home-shopping), voice-over-IP (VOIP), and/orother telephone or data services. The VSE system 102 may reside at aheadend, or other locations such as a hub or node. The VSE system 102may receive content from sources external to the VSE system 102 orsubscriber television network 100 via a wired or wireless (e.g.,satellite or terrestrial network), such as from content providers, andin some embodiments, package-selected national or regional content withlocal programming (e.g., including local advertising) for delivery tosubscribers.

In one embodiment, the VSE system 102 comprises one or more encodingdevices that encodes locally- and/or remotely-provided audiovisualcontent (including data) according to the syntax and semantics of avideo and/or audio coding standard or specification, such as MPEG-2,Advanced Video Coding (AVC), etc. In one implementation, the encodedaudiovisual content for a single program may be carried in a singleMPEG-2 program stream (e.g., one or more packetized elementary stream(PES) packet streams sharing a common time base), and in otherimplementations, the encoded audiovisual content for multiple programsmay be carried as multiple MPEG-2 programs that are multiplexed into anMPEG-2 transport stream, each MPEG-2 program associated with its ownrespective time base. It should be understood that, although MPEG-basedvideo encoding and transport is described throughout the disclosure,encoding and transport according to other specifications and/orstandards (including proprietary mechanisms) may similarly benefit fromthe TSE systems 200 described herein and hence are contemplated to bewithin the scope of the disclosure.

In IPTV implementations, the program or transport stream is furtherencapsulated in Internet protocol (IP) packets, and delivered viamulticast (e.g., according to protocols based on Internet GroupManagement Protocol (IGMP), among other protocols), or in the case ofvideo-on-demand (VOD), via unicast (e.g., Real-time Streaming Protocolor RTSP, among other protocols). For instance, multicast may be used toprovide multiple user programs destined for many different subscribers.In some implementations, unicast delivery may serve as an intermediaryvideo stream delivery mechanism when switching among multicast groups.

In some embodiments, the VSE system 102 may also comprise othercomponents, such as QAM modulators, routers, bridges, Internet ServiceProvider (ISP) facility servers, private servers, on-demand servers,channel change servers, multi-media messaging servers, program guideservers, gateways, multiplexers, and/or transmitters, among otherequipment, components, and/or devices well-known to those havingordinary skill in the art. Further, communication of IP packets betweenthe VSE system 102 and the VSRP system 106 may be implemented accordingto one or more of a plurality of different protocols or communicationmechanisms, such as User Datagram Protocol (UDP)/IP, TransmissionControl Protocol (TCP)/IP, transport packets encapsulated directlywithin UDP or Real-time Transport Protocol (RTP) packets, among others.

The communications medium 104 may comprise a single network, or acombination of networks (e.g., local and/or wide area networks). Forinstance, the communications medium 104 may comprise a wired connectionor wireless connection (e.g., satellite, wireless LAN, etc.), or acombination of both. In the case of wired implementations,communications medium 104 may comprise a hybrid-fiber coaxial (HFC)medium, coaxial, optical, twisted pair, etc. Other networks arecontemplated to be within the scope of the disclosure, includingnetworks that use packets incorporated with and/or compliant to othertransport protocols or standards or specifications.

The VSRP system 106 (also referred to herein as a digital receiver orprocessing device) may comprise one of many devices or a combination ofdevices, such as a set-top box, television with communicationcapabilities, cellular phone, personal digital assistant (PDA), or othercomputer or computer-based device or system, such as a laptop, personalcomputer, DVD/CD recorder, among others. As set forth above, the VSRPsystem 106 may be coupled to the display device 108 (e.g., computermonitor, television set, etc.), or in some embodiments, may comprise anintegrated display (with or without an integrated audio component).

FIG. 2 is an example embodiment of select components of a VSRP system106 comprising an embodiment of TSE system 200. It should be understoodby one having ordinary skill in the art that the VSRP system 106 shownin FIG. 2 is merely illustrative, and should not be construed asimplying any limitations upon the scope of the disclosure. In oneembodiment, the TSE system 200 may comprise all components shown in, ordescribed in association with, the VSRP system 106. In some embodiments,the TSE system 200 may comprise fewer components, such as those limitedto facilitating and implementing the decoding of compressed videostreams. In some embodiments, functionality of the TSE system 200 may bedistributed among the VSRP system 106 and one or more additionaldevices.

The VSRP system 106 includes a communication interface 202 (e.g.,depending on the implementation, suitable for coupling to the Internet,a coaxial cable network, an HFC network, wireless network, etc.) coupledto a demultiplexer 204 (hereinafter, referred to also as a demux 204).The demux 204 is configured to identify and extract information in thevideo stream (e.g., transport stream) to facilitate the identification,extraction, and processing of the compressed pictures. Such informationincludes Program Specific Information (PSI) (e.g., Program Map Table(PMT), Program Association Table (PAT), etc.) and parameters orsyntactic elements (e.g., Program Clock Reference (PCR), time stampinformation, payload_unit_start_indicator, etc.) of the transport stream(including packetized elementary stream (PES) packet information). Inone embodiment, the demux 204 is configured with programmable hardware(e.g., PES packet filters). In some embodiments, the demux 204 isconfigured in software, or a combination of hardware and software.

The demux 204 is coupled to a bus 205 and to a media engine 206. Themedia engine 206 comprises, in one embodiment, decoding logic comprisingone or more of a respective audio decoder 208 and video decoder 210. Themedia engine 206 is further coupled to the bus 205 and to media memory212, which in one embodiment comprises one or more buffers fortemporarily storing compressed and/or reconstructed pictures. In someembodiments, the buffers of the media memory 212 may reside in othermemory (e.g., memory 222, explained below).

The VSRP system 106 further comprises additional components coupled tobus 205. For instance, VSRP system 106 further comprises a receiver 214configured to receive user input (e.g., via direct-physical or wirelessconnection via a keyboard, remote control, voice activation, etc.) toconvey a user's request or command (e.g., for program selection, streammanipulation such as fast forward, rewind, pause, channel change, etc.),one or more processors (one shown) 216 for controlling operations of theVSRP system 106, and a clock circuit 218 comprising phase and/orfrequency locked-loop circuitry to lock into system clock information(e.g., program clock reference, or PCR, which is used to reconstruct thesystem time clock (STC) at the VSRP system 106) received in the videostream (e.g., adaptation field of the transport stream) to facilitatedecoding operations and to clock the output of reconstructed audiovisualcontent. In some embodiments, clock circuit 218 may comprise plural(e.g., independent or dependent) circuits for respective video and audiodecoding operations. Although described in the context of hardwarecircuitry, some embodiments of the clock circuit 218 may be configuredas software (e.g., virtual clocks) or a combination of hardware andsoftware. Further, in some embodiments, the clock circuit 218 isprogrammable.

The VSRP system 106 further comprises a storage device 220 (andassociated control logic) to temporarily store buffered content and/ormore permanently store recorded content. Memory 222 in the VSRP system106 comprises volatile and/or non-volatile memory, and is configured tostore executable instructions or code associated with an operatingsystem 224, and one or more applications 226 (e.g., interactiveprogramming guide (IPG), video-on-demand (VOD), personal video recording(PVR), WatchTV (associated with broadcast network TV), among otherapplications such as pay-per-view, music, driver software, etc.).

Further included in one embodiment in memory 222 is extrapolation logic228, which in one embodiment is configured in software. In someembodiments, extrapolation logic 228 may be configured in hardware, or acombination of hardware and software. The extrapolation logic 228,described further below, is responsible for computing extrapolatedvalues for presentation and/or decoding time stamps for cached orbuffered compressed pictures that are without associated time stampinformation (e.g., PTS or DTS values). Explicit PTS/DTS values andextrapolated values (for PTS and DTS) are compared to the reconstructedSTC (generated by the clock circuit 218) to enable a determination ofwhen the buffered compressed pictures are provided to the video decoder210 for decoding (DTS) and when the buffered, decoded pictures areoutput by the video decoder 210 (PTS) to display and output logic 230for processing and subsequent presentation on a display device 108.

The VSRP system 106 is further configured with the display and outputlogic 230, as indicated above, which includes graphics and videoprocessing pipelines as known in the art to process the decoded picturesand provide for presentation (e.g., display) on display device 108. Acommunications port 232 (or ports) is further included in the VSRPsystem 106 for receiving information from and transmitting informationto other devices. For instance, the communication port 232 may featureUSB (Universal Serial Bus), Ethernet, IEEE-1394, serial, and/or parallelports, etc. The VSRP system 106 may also include an analog video inputport for receiving analog video signals.

One having ordinary skill in the art should understand that the VSRPsystem 106 may include other components not shown, including a tuningsystem with one or more tuners, demodulators, compression engine,memory, decryptors, samplers, digitizers (e.g., analog-to-digitalconverters), multiplexers, conditional access processor and/orapplication software, driver software, Internet browser, among others.Further, though the extrapolation logic 228 is illustrated as residingin memory 222, it should be understood that such logic 228 may beincorporated in the media engine 206 in some embodiments, or elsewhere.Similarly, in some embodiments, functionality for one or more of thecomponents illustrated in, or described in association with, FIG. 2 maybe combined with another component into a single integrated component ordevice.

Having described an example embodiment for a VSRP system 106, attentionis directed to FIGS. 2 and 3 where select components and correspondingprocessing from the TSE system 200 are further explained. As set forthabove, the VSRP system 106 includes a communication interface 202configured to receive an audiovisual program (e.g., on-demand orbroadcast program) delivered as, among other media content components, asequence of compressed pictures of a video stream. The discussion thatfollows assumes a stream transition event corresponding to a user- orsystem-prompted channel change event (e.g., the channel changeimplemented to go from one multicast group to another via a channelchange server located at the VSE system 102 or elsewhere), resulting inthe transmittal and subsequent reception and processing of a singleprogram transport stream in the context of an IPTV environment. Itshould be appreciated that the TSE system embodiments disclosed hereinare not limited to channel change implementations, but also contemplateother stream transition events (e.g., VOD and stream manipulation, localadvertisement insertion, etc.) and/or non-IPTV environments (e.g.,dedicated transmissions) that may share one or more of the scenarios setforth in the beginning of the disclosure or have conditions that the TSEsystem embodiments can remedy or mitigate.

In addition, the parameters the TSE system embodiments detect in thetransport stream (including the PES packets) to facilitateidentification and extraction are based on an assumption of MPEG-basedtransport. However, it should be appreciated that systems in which timestamp information and other identifying parameters are conveyed by othermechanisms (e.g., not extracted from a transport stream or PES packet)may also benefit from the concepts disclosed herein and hence arecontemplated to be within the scope of the disclosure. For instance,time stamp information may reside in a packet header for whichapplication software in the VSRP system 106 is configured to receive andprocess in some embodiments (i.e., without extraction from a transportstream).

With reference to FIG. 3, shown is a block diagram that illustrates avideo stream 300 comprising a sequence (in transmission order) ofcompressed pictures (such as conveyed over communications medium 104 asa transport stream encapsulated in IP), the compression denoted by a “C”prefix to the picture type (e.g., “CB” is a compressed “B” picture, “CI”is a compressed “I” picture, etc.). Although the video stream 300 isillustrated in FIG. 3 as possessing a particular picture sequencepattern (e.g., IBBPB . . . PBBI) common to an MPEG-2 group of pictures(GOP), it should be understood that other picture sequence patterns arecontemplated to be within the scope of the disclosure. The channelchange is denoted by arrow 304. Further, the highlighted compressedpictures 302, 306, and 308 (denoted in FIG. 3 by heavier borderthickness, such as for the first and last “CB” pictures and the “CP”picture) symbolize pictures that possess or are otherwise associatedwith time stamp information (explicit time stamp information), whereasthe non-highlighted pictures (e.g., CI 312, CB 314, CB 316, etc.) haveno associated time stamp information at the present snapshot in time(pre-extrapolation) represented by FIG. 3.

In one embodiment, the TSE system 200 backwards extrapolates time stampinformation (explicitly received in the video stream 300) according to abackwards extrapolation period (BEP), as described further below. Ingeneral, certain compressed pictures (compressed pictures 312, 314, and316) are received and cached (e.g., buffered) by the TSE system 200, andsuch pictures have no corresponding time stamp information when cached.At a time corresponding to receiving the first picture, since thechannel change event, that has explicit time stamp information (e.g.,compressed picture 306), the TSE system 200 backwards extrapolates theexplicit time stamp information according to a fixed, or in someembodiments configurable, BEP to derive time stamp information for oneor more of the cached pictures 312, 314, 316 received and retained in abuffer (e.g., in media memory 212) prior to compressed picture 306.

FIGS. 4A-4B illustrate timing diagrams 400A and 400B, respectively,corresponding to some example BEP embodiments. In one embodiment, theBEP may be a fixed parameter stored locally in the VSRP system 106(e.g., as programmed at the time of start-up or manufacture), and insome embodiments, the BEP may be programmable or otherwise configurable(e.g., based on signaling from a remote location, such as via systemoperator input, based on parameters in the received video stream, and/orbased on local input from a user or service technician via a displayedinterface of selectable BEP options). In one embodiment, referring todiagram 400A of FIG. 4A, the start 402 of the BEP 410A corresponds tothe locking of the PCR received in the video stream (e.g., in theadaptation field of the transport stream) for the associated audiovisualprogram. For instance, responsive to the channel change event 304, thedemux 204 receives information (e.g., a PMT) in the transport streamthat the demux 204 uses to identify the PIDs of the video, audio, and/ordata streams corresponding to the requested video program. Theidentification may further serve to assist the demux 204 in rejectingsecondary audio programs (SAPs) that are not required. In someembodiments, the appropriate PMT packet may be identified by atransmitted PAT, whereas in some embodiments, the PAT is not required(e.g., since the PMT is known a priori).

Responsive to the information (e.g., of the PMT, which signals thepacket location of the PCR), the demux 204 parses the transport streamand extracts the PCR value from the identified packet and communicatesthe extracted PCR value and time corresponding to the associated packetarrival to the clock circuit 218, the extrapolation logic 228, and themedia engine 206. In one embodiment, the clock circuit 218 locks to thePCR, and the extrapolation logic 228 initiates the BEP 410A. Forinstance, in one embodiment, the media engine 206 uses the arrival timeof the transport stream packet carrying the PCR value and the PCR valueitself to adjust control elements of the clock circuit 218. The demux204 continues to parse packets of the transport stream and extract thepackets corresponding to the compressed pictures for the requested videoprogram, and the compressed pictures are stored in media memory 212. Asexplained above, in the present example, compressed pictures 312, 314,and 316 do not have associated time stamp information (e.g., are missingan associated PTS or PTS/DTS). The extrapolation logic 228 defines theend 404 of the BEP 410A based on the extraction of the compressedpicture 306, which comprises explicit time stamp information (e.g.,possesses or is associated with a PTS) carried in one embodiment in thePES packet header corresponding to compressed picture 306. Theextrapolation logic 228 then performs backwards extrapolation accordingto the BEP 410A in a manner as explained further below.

In the embodiment illustrated in the diagram 400B of FIG. 4B, theextrapolation logic 228 defines the end 404 of the BEP 410B in themanner similar to that described above in association with FIG. 4A(e.g., based on reception of explicit time stamp information), anddetermines a start 406 based on the point of ingestion or acquisition ofthe video program. For instance, one parameter the extrapolation logic228 uses to start the BEP 410B is the payload_unit_start_indicatorcarried in the transport stream header. When thepayload_unit_start_indicator is set to a value of 1, this is anindication that the MPEG-2 transport stream packet's payload fieldbegins with the first byte of an MPEG-2 PES packet under the constraintthat only a single MPEG-2 PES packet may begin in a transport streampacket, hence enabling identification of the start of a picture oraccess unit. The extrapolation logic 228 performs backwardsextrapolation based on the determined start 406 and completion 404 ofthe BEP 410B in a manner as explained further below. The detection ofthe payload_unit_start_indicator enables the determination of the BEP410B without the locking of the PCR, and thus may enable a shorter delayin decoding and presentation for the requested video program.

Note that in some embodiments, the PMT may be cached in advance for eachchannel (e.g., physical or logical channel) that was previouslyaccessed, and hence, the compressed pictures may be cached responsive tothe channel change event without seeking to detect the PMT (since it isknown and cached in advance). In other words, the BEP 410 may beinitiated even further back in time than the above-described embodimentsby detection of the payload_unit_start_indicator without seeking the PMTresponsive to the stream transition event.

Regardless of the method used by the extrapolation logic 228 to definethe BEP 410, the extrapolation logic 228 performs backwardsextrapolation to compute the PTS/DTS values (e.g., based on using theframe or picture rate and the picture types received so far) for thecompressed pictures it has received but not decoded yet (i.e.,compressed 312, 314, and 316). In one embodiment, the extrapolationlogic 228 determines the out-of-orderness (PTS-to-DTS relationship)based on the recorded picture type and a record of the picture sequencepattern (e.g., GOP structure) used in the video stream. The picturesequence pattern may be determined from previous access to the channelfor the requested video program, from industry practice (e.g., MPEG-2video typically uses a common GOP structure), or according to othermechanisms.

Note that a source of delay is defined by DTS-PCR. If the video decoder210 waited to fill the buffer (e.g., in media memory 212, such as avideo bit-buffer in MPEG-2 or compressed picture buffer in AVC), theremay be a longer channel change time since the first determined DTS (atthe time of receiving the first PTS) is farther out in time (in relationto PCR) since video coding imparts a DTS-PCR delay for rate managementpurposes and to avoid bit-buffer underflow. Besides, because of theconstant bit rate (CBR) channel practiced in IPTV, each picture has aDTS-PCR delay of approximately equal to the GOP size (typically half asecond for MPEG-2 video, or one (1) second or more for AVC). The DTS-PCRdelay is also referred to as an initial bit buffer delay. In essence,the TSE system 200, by backwards extrapolating the PTS values, canreduce or eliminate the initial bit buffer delay that may have beenincurred after obtaining the first DTS.

Because the extrapolation logic 228 performs backwards extrapolation oftime stamp information for the previously cached or buffered compressedpictures, then such compressed and buffered pictures can be decoded andoutput for subsequent presentation. In one embodiment, such compressedand buffered pictures can be decoded and output if their respectivelycorresponding determined DTS (computed according to the extrapolated PTSand inferred picture sequence pattern) is greater than or equal to theSTC value. In some embodiments, explained further below, output andpresentation occurs despite the expiration of the extrapolated PTS/DTSvalues.

In some cases, the first displayed picture is an I-picture and sometimesit is not. In either case, from the user's perspective, the channelchange time may be reduced since one approach of the TSE system 200allows the video decoder 210 to present for display the pictures beforeit receives an I-picture whose time stamp information (e.g., PTS/DTS) isknown.

With regard to the above-referenced embodiments where output andpresentation is conditioned on whether the backwards extrapolatedPTS/DTS values have expired, the selection of pictures for decoding andoutput is illustrated in the examples presented in the diagrams 500A and500B of FIGS. 5A and 5B, respectively. Assume there are compressedpictures in the picture sequence pattern of the video stream 300 of FIG.3 that are already received and whose extrapolated (or inferred) PTSdeadlines have not yet been reached (e.g., the PTS/DTS values have notexpired when compared to the reconstructed STC values). In such ascenario, the video decoder 210 starts decoding the pictures that itpreviously did not decode (e.g., compressed pictures 312, 314, 316,etc.) and presents for display (e.g., via display and output logic 230)the pictures based on the extrapolated PTS deadlines. In the examplediagram 500A shown in FIG. 5A, if none of the earlier pictures' PTSdeadlines have expired by the time the backward extrapolation iscomplete, and the earlier pictures are decoded, all decoded pictures(extending back to that associated with compressed picture 312) can bepresented for display.

Referring to FIG. 5B, an example is shown where the PTS deadlines forthose pictures corresponding to compressed pictures 312 and 314 (i.e.,located in the column beneath 314 and 316 in diagram 500B) have expired.In other words, in this example, only the “B” picture, located in thecolumn in diagram 500B beneath compressed “B” picture 316, has abackwards extrapolated PTS/DTS value that has not expired (e.g., greaterthan or equal to the STC value). Accordingly, in this embodiment, onlyone picture having the backwards extrapolated PTS/DTS value is outputfor presentation.

In the worst case, the video decoder 210 cannot decode the firstI-picture it receives, and hence it waits until the next I picture.Hence, the channel change time difference between the best (FIG. 5A) andworst case scenarios is one GOP duration for the present examplecorresponding to FIG. 3, which practically speaking, can range in someembodiments from 500 milliseconds (ms) to a few seconds. As noted, FIG.5B represents an intervening case (between best and worst).

With regard to another embodiment referenced above, an output andpresentation result may follow in accordance with a best case condition(e.g., FIG. 5A) regardless of expiration of the backwards extrapolatedPTS/DTS values. In such embodiments, the TSE system 200 operates withdecoding functionality that employ clock circuits 218 configured forprogrammable system time clock (STCs) operation. For a given BEP, theTSE system 200 directs its attention to the first decodable picture(hereinafter referred to PIC1 for brevity in explanation) for which aPTS/DTS value has been backwards extrapolated. If the backwardsextrapolated value of PTS/DTS for PIC1 has expired, instead ofdiscarding PIC1 and any subsequent pictures (i.e., “late” pictures thatalso have expired PTS/DTS values), the STC may be “rewound” (orgenerally, reconfigured) to cause the STC value to be equal to the DTSvalue of PIC1. In this manner, PIC1 (and any subsequent late pictures)may be output for presentation. In such an embodiment, there may be noadded advantages in terms of channel change time, but bit-buffer sizemay increase to accommodate pictures that, without this technique, wouldhave been discarded. Further, a difference between the PCR and the localSTC may be introduced (e.g., in view of the negative time offset to theSTC). However, in some implementations, equality in the values of STCand PCR may not be strictly adhered to nor required (e.g., insoftware-controlled STC provision), and hence, it is often sufficientfor the STC rate to follow the PCR rate (e.g., with a constant offset).

In some embodiments, the STC is rewound to a value sufficient to enabledecoding and display of the first and subsequent decodable pictures inthe buffer (e.g., STC value at least equal to the DTS value or PTS valueif the DTS value is not calculated). In some embodiments, in view of thepotential buffer and/or offset implications noted above, the amount ofrewind of the STC may be the minimum of the following: the time offsetbetween the DTS of the first decodable picture in the buffer and thevalue of the STC at the time the TSE is complete, the amount of freespace in the bit buffer in terms of time (e.g., free buffer size/streambit-rate), and the maximum amount of time shift, with respect toreal-time, that is tolerable.

The TSE system 200 may be implemented in hardware, software, firmware,or a combination thereof. To the extent certain embodiments of the TSEsystem 200 or a portion thereof are implemented in software or firmware,executable instructions for performing one or more tasks of the TSEsystem 200 are stored in memory or any other suitable computer readablemedium and executed by a suitable instruction execution system. In thecontext of this document, a computer readable medium is an electronic,magnetic, optical, or other physical device or means that can contain orstore a computer program for use by or in connection with a computerrelated system or method.

To the extent certain embodiments of the TSE system 200 or a portionthereof are implemented in hardware, the TSE system 200 may beimplemented with any or a combination of the following technologies,which are all well known in the art: a discrete logic circuit(s) havinglogic gates for implementing logic functions upon data signals, anapplication specific integrated circuit (ASIC) having appropriatecombinational logic gates, programmable hardware such as a programmablegate array(s) (PGA), a field programmable gate array (FPGA), etc.

Having described various embodiments of TSE system 200, it should beappreciated that one method embodiment 600, implemented in oneembodiment by logic (hardware, software, or a combination thereof) ofthe TSE system 200 and shown in FIG. 6, comprises receiving a videostream comprising a first compressed picture without associated timestamp information and a second compressed picture having associatedfirst time stamp information, the second compressed picture followingthe first compressed picture in transmission order (602), derivingsecond time stamp information based on the first time stamp information(604), and processing the first compressed picture based on the secondtime stamp information (606).

Any process descriptions or blocks in flow charts or flow diagramsshould be understood as representing modules, segments, or portions ofcode which include one or more executable instructions for implementingspecific logical functions or steps in the process, and alternateimplementations are included within the scope of the present disclosurein which functions may be executed out of order from that shown ordiscussed, including substantially concurrently or in reverse order,depending on the functionality involved, as would be understood by thosereasonably skilled in the art. In some embodiments, steps of a processidentified in FIG. 6 using separate boxes can be combined. Further, thevarious steps in the flow diagrams illustrated in conjunction with thepresent disclosure are not limited to the architectures described abovein association with the description for the flow diagram (as implementedin or by a particular module or logic) nor are the steps limited to theexample embodiments described in the specification and associated withthe figures of the present disclosure. In some embodiments, one or moresteps may be added to one or more of the methods described in FIG. 6,either in the beginning, end, and/or as intervening steps.

It should be emphasized that the above-described embodiments of thepresent disclosure are merely possible examples of implementations,merely set forth for a clear understanding of the principles of the TSEsystems and methods. Many variations and modifications may be made tothe above-described embodiment(s) without departing substantially fromthe spirit and principles of the disclosure. Although all suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and protected by the following claims, thefollowing claims are not necessarily limited to the particularembodiments set out in the description.

We claim:
 1. A method, comprising: receiving indication of a streamtransition event; deriving time stamp information based at least in partlocating a predetermined backward extrapolation period (BEP) value; anddetermining whether the derived time stamp information has expired, andresponsive to the determination, reconfiguring a system time clock tomatch the value to enable processing of the stream transition event. 2.The method of claim 1, wherein the stream transition event comprisesstream manipulation for a video on demand application.
 3. The method ofclaim 1, wherein the stream transition event comprises advertisementinsertion.
 4. The method of claim 1, wherein the stream transition eventcomprises one of a user-prompted channel change event and asystem-prompted channel change event.
 5. The method of claim 1, furthercomprising deriving the timestamp information for one or more cachedpictures with no corresponding time stamps.
 6. The method of claim 1,further comprising determining whether the derived time stampinformation has expired, wherein the processing is responsive to thevalue corresponding to the second time stamp information not havingexpired.
 7. The method of claim 1, wherein the BEP corresponds to thelocking of a received program clock reference (PCR).
 8. The method ofclaim 1, wherein the PCR was received in an adaptation field of a streaminvolved in the stream transition event.
 9. The method of claim 1,wherein the stream transition event occurs in an IPTV environment. 10.The method of claim 1, wherein the derived time stamp informationcorresponds to a received, but not decoded, picture.
 11. The method ofclaim 10, further comprising decoding the received picture based atleast in part on the derived time stamp information.
 12. The method ofclaim 11, further comprising preparing the received picture forpresentation based at least in part on the derived time stampinformation.
 13. A system, comprising: a processing device configuredto: receive a transport stream comprising plural compressed pictures ofa video steam, the compressed pictures comprising a first portion ofcompressed pictures with no corresponding presentation time stamp (PTS)assignment and a second portion comprising at least one compressedpicture following the first portion in transmission order, the at leastone compressed picture comprising a first PTS; backwards extrapolate thefirst PTS to derive an extrapolated PTS value for each respectivecompressed picture of the first portion; determine whether theextrapolated PTS value has expired, and responsive to the determination,reconfiguring a system time clock to match the value to enableprocessing of a stream transition event; and process the streamtransition event based on the extrapolated PTS values.
 14. The system ofclaim 13, wherein the processing device is further configured to startbackward extrapolation based on a backward extrapolation period (BEP)started by an indicator contained in a header of the transport stream.15. The system of claim 14, wherein determination of the indicatorenables determination of the BEP without locking a program clockreference (PCR).
 16. The system of claim 14, wherein determination ofthe indicator enables determination of the BEP without seeking a cached(PMT) responsive to the stream transition event.
 17. The system of claim13, wherein the processing device is configured to determine a decodingtime stamp (DTS) based on the extrapolated PTS.
 18. The system of claim13, wherein the processing device is further configured to eitherprocess the first portion corresponding exclusively to an unexpiredvalue or unexpired values or process the first portion associated withreconfigured system time clock values.
 19. The system of claim 13,further comprising a display device, wherein the processing device isconfigured to process by decoding the at least part of the first portionand preparing the decoded first part for display on the display device.20. A system, comprising: means for buffering a media content streamcomprising a first compressed media content without associated timestamp information and a second compressed media content havingassociated first time stamp information, the second compressed mediacontent following the first compressed media content in transmissionorder; means for determining whether the second time stamp informationhas expired and, responsive to the determination, reconfiguring a systemtime clock to match the second time stamp information; and means forcomputing second time stamp information based on the first time stampinformation and processing a stream transition event based on the secondtime stamp information.